Mitsubishi Air Conditioner Error Code MT1

MT1 is a maintenance signal output indicating that the inverter's cumulative energization time has reached or exceeded the value programmed in parameter Pr.504. It is a scheduled maintenance reminder, not a component failure. The system is designed to raise this alert so technicians can perform preventive service before a real fault develops. Once the required maintenance is done, the timer counter should be reset to clear the signal.

MT1 is a maintenance reminder rather than an active fault, so the unit will generally continue to operate. However, ignoring the signal defeats the purpose of the scheduled maintenance program, which is to catch component wear before it causes a real failure. Continuing to run the system without completing the indicated maintenance could eventually lead to inverter damage or an unplanned shutdown.

The cost depends on what maintenance tasks are required based on the Pr.504 program at your site. A basic inspection and timer reset by a technician may range from around 75 to 150 dollars. If components such as the inverter cooling fan or capacitors need replacement, costs can range from 150 to 500 dollars or more depending on parts and labor rates in your area.

Fixing the MT1 signal requires completing whatever maintenance task was intended when Pr.504 was configured. This typically involves inspecting and servicing components such as the inverter cooling fan, capacitors, or filters. After completing the maintenance, the cumulative energization timer counter must be reset through the parameter settings to clear the MT1 output and restart the interval countdown.

A simple power cycle or reset of the air conditioner will not clear the MT1 signal because the trigger is based on the cumulative energization counter stored in parameter Pr.504. The counter must be reset through the inverter parameter settings after maintenance is completed. Until the counter is cleared, the MT1 signal will persist.